Course of Raku / Objects, I/O, and exceptions / Exceptions

The CATCH phaser

The try block is convenient, but it treats the whole block as one unit: either it works or it does not. The CATCH phaser gives you finer control — it lets you handle an exception inside the block where it happened, and decide what to do.

CATCH is a phaser, like the ones you met in the section about control flow. You write it anywhere inside a block; it runs only if an exception is thrown there. The exception is available as the topic $_:

{
    die 'Boom!';

    CATCH {
        default {
            say 'Caught: ' ~ .message;
        }
    }
}

say 'after';

The program prints:

Caught: Boom!
after

The default block inside CATCH handles any exception. Once it has run, the exception is considered handled, so the program does not stop — execution carries on after the enclosing block, which is why after is printed.

Without the CATCH, the die would have ended the program before after could be reached.

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